1. Field of the Invention
The present invention relates to a thin film magnetic head having an inductive-type magnetic transducer for writing and a method of manufacturing the same.
2. Description of the Related Art
Improvements in the performance of a thin film magnetic head have been sought since an areal density of a hard disk drive has been improved. A composite thin film magnetic head having a structure, in which a recording head having an inductive-type magnetic transducer for writing and a reproducing head having a magnetoresistive (hereinafter referred to as MR) element for reading are stacked, is widely used as the thin film magnetic head.
FIGS. 25A and 25B show an example of a cross sectional structure of a conventional thin film magnetic head. This thin film magnetic head includes, for example, a substrate 101 formed of altic (aluminum oxide and titanium carbide; Al2O3. TiC), an insulating layer 102 formed of aluminum oxide (Al2O3; hereinafter simply referred to as “alumina”), a bottom shield layer 103 formed of ferronickel alloy (NiFe; hereinafter simply referred to as “permalloy” (trade name)), shield gap films 104 and 106 for burying an MR film 105, a top shield layer serving as a bottom pole (hereinafter simply referred to as a “bottom pole”) 107, a write gap layer 108 having an opening 108K, a thin film coil 109 formed of copper (Cu) for generating magnetic flux, an insulating layer 110 formed of photoresist for insulating the thin film coil 109 from the adjacent elements, a top pole 111 magnetically coupled to the bottom pole 107 through the opening 108K and forming a propagation path for magnetic flux (magnetic path) with the bottom pole 107, and an overcoat layer 112 serving as a cap film, stacked in this order from the bottom. The shield gap films 104 and 106, the write gap layer 108, and the overcoat layer 112 are formed of, for example, a material similar to that of the insulating layer 102, and the bottom pole 107 and the top pole 111 are formed of, for example, a material similar to that of the bottom shield layer 103.
The top pole 111 and the bottom pole 107 have the same uniform width in the vicinity of the write gap layer 108 located in a region closer to a recording-medium-facing surface (air bearing surface) 120 facing a magnetic recording medium (hereinafter simply referred to as a “recording medium”), and these portions form a pole portion 200 defining a recording track width. This pole portion 200 is formed by, for example, forming the top pole 111 having an uniform width portion (a tip portion 111A) constituting part of the pole portion 200, and then etching the write gap layer 108 and the bottom pole 107 in a self-aligned manner with use of the tip portion 111A as a mask.
Enhancing especially the recording density of the recording head among various performances requires miniaturization of the width of the pole portion 200 (magnetic pole width) to the order of submicrons to increase the track density at the recording medium. For this purpose, the magnetic pole width is preferably made uniform with high precision throughout the pole portion 200. This is because a magnetic pole having a partially greater width causes a side erase, i.e. causing data to be written not only in a track area intended for writing but also in the adjacent track areas, thereby overwriting and erasing information already written in the adjacent track areas.
However, although such miniaturization of the magnetic pole width to the order of submicrons is required, it has been difficult to form the tip portion 111A of the top pole 111 used as a mask for forming the pole portion 200 with high precision because of the reasons below.
When, for example, the thin film coil 109 is first formed on a planar layer lying thereunder (such as the write gap layer 108) and covered with the insulating layer 110, a hill portion (hereinafter referred to also as an “apex portion”) of photoresist is formed on the planar underlying layer. The surface of the apex portion in the vicinity of an edge thereof is fluidized by a heat treatment performed on the photoresist to fill in each gap between turns of the thin film coil 109, and therefore this surface is formed as a rounded slope. When the top pole 111 formed of a plated film pattern is provided in a region having an irregular structure resulting from the apex portion and the like, light is reflected horizontally or obliquely from the underlying slope when an exposure process is performed on the photoresist film formed in the irregular structure region during a process of forming a framework (frame pattern) used for forming the plated film pattern. Such reflected light decreases the precision of forming the frame pattern because the reflected light increases or decreases the region in the photoresist film exposed to light. This results in a similar decrease in precision of forming the tip portion 111A of the top pole 111 having a very small width.
Such a decrease in precision of forming the top pole 111 is determined based on, for example, the height of the apex portion from the underlying layer, and the decrease becomes more prominent as an apex angle α1, which is one of the factors determining the performance of the recording head, is increased. The apex angle α1 is an angle between the tangent line to the slope of the insulating layer 10 covering the thin film coil 109 located closer to the air bearing surface 120 side and the surface of the planar underlying layer (write gap layer 108). In the conventional thin film magnetic head shown in FIG. 25A and FIG. 25B, if a sufficient thickness is provided to the part of the insulating layer 110 located over the thin film coil 109 for the sake of electrical isolation between the thin film coil 109 and the top pole 111, the slope of the insulating layer 110 located at the vicinity of its edge becomes steep, resulting in a greater apex angle α1.
FIG. 26A and FIG. 26B show an example of an approach for suppressing the decrease in precision of forming the top pole 111 resulting from an increase in the apex angle α1. FIG. 26A and FIG. 26B are cross sectional views showing a structure of another conventional thin film magnetic head. In this thin film magnetic bead, the insulating layer 110 burying the thin film coil 109 is, for example, composed of two insulating elements (insulating layer portions 110A and 110B). The thin film coil 109 is disposed on the insulating layer portion 110A having a surface formed as a relatively gentle slope in the vicinity of an edge thereof, and the insulating layer portion 110B is disposed so that its edge on the air bearing surface 120 side is recessed to the edge of the insulating layer portion 110A on the air bearing surface 120 side. Although such a configuration can reduce an apex angle α2 as compared to the apex angle in the conventional example shown in FIG. 25A and FIG. 25B (α2<α1), a step is created in the thickness direction between the insulating layers 110A and 110B. Such a step in the insulating layer 110 increases the amount of light reflected in the horizontal direction from the slope of the insulating layer portion 110B in the stepped portion located on the air bearing surface 120 side during the exposure process for forming the frame pattern, thereby making it difficult to improve the precision of forming the top pole 111. In addition, the step in the insulating layer 110 causes disturbance in magnetic flux inside the top pole 111 at a portion corresponding to the step, leading to a possible decrease in recording characteristics and the like.
Besides the above-described conventional example, various other specific examples are proposed as an approach of reducing the apex angle to enhance the precision of forming the uniform width portion (tip portion) of the top pole. Japanese Patent Laid-Open Publication No. 2000-251220, for example, discloses an approach in which an insulating layer covering the thin film coil is composed of three insulating layer elements (an apex angle setting insulating layer, an insulating layer for setting a raising angle located on the side of the center of the coil, and a covering insulating layer), and the covering insulating layer having a great thickness and covering the thin film coil partially overlaps the apex angle setting insulating layer having a small thickness (height) disposed isolated from the thin film coil. As in the conventional example shown in FIG. 26A and FIG. 26B, although this approach makes it possible to provide a relatively small apex angle, a step is created by the apex angle setting insulating layer and the covering insulating layer, and therefore it is difficult to achieve the above-described objects, that is, improving the precision of forming the top pole layer and securing stable recording characteristics and the like.
Further, Japanese Patent Laid-Open Publication No.2000 -207711 discloses, for example, an approach in which the insulating layer covering the coil layer is composed of three insulating layer elements (first, second, and third insulating layers), and after the first insulating layer, the coil layer, and the second insulating layer are formed in this order, the third insulating layer is provided filing in the stepped region formed by the first and second insulating layers, so that a continuous slope is created by the first, second, and third insulating layers. This approach enables to avoid creation of a step in the insulating layer and therefore suppress decrease in recording characteristics and the like resulting from the step as pointed out in connection with the Japanese Patent Laid-Open Publication No. 2000-251220. However, as the thickness (height) of the entire insulating layer is determined by the sum of the thicknesses of the first and second insulating layers, a relatively great apex angle is provided, making it difficult to improve the precision of forming the top pole.